In optical fiber communications, connectors for joining fiber segments at their ends, or for connecting optical fiber cables to active or passive devices, are an essential component of virtually any optical fiber system. The connector or connectors, in joining fiber ends, for example, has, as its primary function, the maintenance of the fiber ends in a butting relationship such that the core of one of the fibers is axially aligned with the core of the other fiber so as to maximize light transmissions from one fiber to the other. Another goal is to minimize back reflections. Such alignment is extremely difficult to achieve, which is understandable when it is recognized that a fiber is 125.0±0.5 microns and that the mode field diameter, of, for examples, a singlemode fiber is approximately nine microns (0.009 mm) and a multimode fiber is 50 microns (0.050 mm). Good alignment (low insertion loss) of the fiber ends is a function of the alignment, the width of the gap (if any) between the fiber ends, and the surface condition of the fiber ends, all of which, in turn, are inherent in the particular connector design. The connector must also provide stability and junction protection and thus it must minimize thermal and mechanical movement effects. These same considerations apply to arrangements where the fiber, terminated in a plug connector, is to be used with active or passive devices, such as, for example, data links for computers or transceivers and the like.
In the present day state of the art, there are numerous, different, connector designs in use for achieving low insertion loss and stability. In most of these designs, typically a pair of ferrules (one in each connector or one in the connector and one in the apparatus or possibly in the device), each containing an optical fiber end which is adhesively bonded or cemented in an axial bore within the ferrule, are butted together end-to-end, and light travels across the junction. The fibers are usually bonded within the ferrules and the adhesive is cured during manufacture to produce a connectorized fiber. It is possible that the ferrule of a connector may also be plugged directly into the bore of a wide area detector or receiver.
In U.S. Pat. No. 6,128,927 of Ahrens, et al, there is shown a method and apparatus for precisely controlling the diameter of the bore in a ferrule. The method comprises producing a ferrule, preferably of glass, having an oversized bore therein. A rod of metal, such as stainless steel, having a diameter substantially the same as the diameter of the fiber to be contained in the ferrule bore, is inserted in the oversized bore and the assembly is heated to collapse the glass ferrule around the rod. The assembly is then cooled, as by dipping in liquid nitrogen, so that the rod may be extracted, leaving a ferrule bore (at normal temperature, having a diameter equal to the diameter of the fiber). This is a production process for manufacturing ferrules, and is unsuitable for use in the field. Additionally, it appears that the fiber, after insertion in the ferrule bore, is cemented in place.
It is desirable that an installer in the field has the capability of replacing a connector on a fiber end, or mounting a connector to a newly created fiber end, as in splicing. Further, in replacing a connector that has been damaged, for example, the faulty connector must simply be cut off and discarded inasmuch as the fiber is cemented therein, and a new connector attached to the now somewhat shortened fiber. In the present state of the art, this means that the installer must have in his kit the adhesive, which if the adhesive is a two-part system, would have a limited pot-life, or an anaerobic adhesive would require the use of a catalyst, or a UV cement that would require a UV curing means therefore, and new fiber connectors (unmounted). Adhesives and cements are messy to handle and can also contaminate the precision outside surface of the ferrule if extreme care is not exercised. From a practical standpoint, adhesive or cement is messy to use; and from an economic standpoint, therefore, it becomes an expensive operation. Elimination of the need to bond the fiber within the ferrule using adhesives or cements, and the concomitant discarding of the connector being replaced, would be highly desirable.